In the current year studies on the incorporation of adenosine-8-H3 into stable RNA of mouse ova have been continued. Small amounts of a concentrated solution of the precursor were injected into the ovarian bursa and ova collected at various subsequent intervals by super- oculation. The most significant parameter affecting the amount of labeled RNA recovered in ova was the interval in days between bursal injection and ovulation. The maximum labeled RNA recovered per ovum was reached when injection preceded ovulation by 19 to 10 days, corresponding to the known major growth phase of the oocyte. Analysis of labeled RNA of ova collected at intervals of 19, 15, 12, 9, and 7 days after bursal injection showed that up to 50% of the label appeared in heterogeneous RNA at the shorter intervals.